Utilizing Moist or Dry Swabs for the Sampling of Nasal MRSA Carriers? An <i>In Vivo</i> and <i>In Vitro</i> Study

<div><p>This study investigates the quantitative bacterial recovery of Methicillin-resistant S<i>taphylococcus aureus</i> (MRSA) in nasal screenings by utilizing dry or moistened swabs within an <i>in vivo</i> and an <i>in vitro</i> experimental setting. 135 nasal MRSA carriers were each swabbed in one nostril with a dry and in the other one with a moistened rayon swab. Quantitative bacterial recovery was measured by standard viable count techniques. Furthermore, an anatomically correct artificial nose model was inoculated with a numerically defined suspension of MRSA and swabbed with dry and moistened rayon, polyurethane-foam and nylon-flocked swabs to test these different settings and swab-materials under identical laboratory conditions. <i>In vivo</i>, quantities of MRSA per nostril in carriers varied between <10¹ and >10⁷ colony forming units, with a median of 2.15x10⁴ CFU. However, no statistically significant differences could be detected for the recovery of MRSA quantities when swabbing nasal carriers with moist or dry rayon swabs. <i>In vitro</i> testing confirmed the <i>in vivo</i> data for swabs with rayon, polyurethane and nylon-flocked tips, since pre-moistening of swabs did not significantly affect the quantities of retrieved bacteria. Therefore, pre-moistening of swabs prior to nasal MRSA sampling provides no advantage in terms of recovering greater bacterial quantities and therefore can be omitted. In addition, this situation can be mimicked in an <i>in vitro</i> model, thereby providing a useful basis for future <i>in vitro</i> testings of new swab types or target organisms for screening approaches.</p></div

Quantities of MRSA per nostril.

<p>Quantities of MRSA per nostril.</p

Recovered MRSA quantities from patients utilizing dry or moistened rayon swabs.

<p>Patients were swabbed in the nostrils utilizing either dry or moist rayon swabs. CFU = colony forming units. Data result from n = 135 patients. p-value = 0.17 (Wilcoxon-Mann-Whitney U-test).</p

Recovered MRSA quantities from the artificial nose model utilizing dry or moist rayon, polyurethane foam and nylon-flocked swabs.

<p>Nose models were swabbed utilizing either dry or moistened rayon, polyurethane foam or nylon-flocked swabs. Data results from n = 10 swabs for each setting. p-value (comparing dry and moist swabs within one swab-type) = 0.62 (Nerbe plus, rayon); 0.90 (MWE, polyurethane); 0.72 (Copan, nylon-flocked); 0.96 (MWE, rayon) (Wilcoxon-Mann-Whitney U-test).</p